Current treatment options for systemic fungal infections remain limited. The development of new antifungals is complicated by the structural and metabolic similarities among fungal and host cells, and the consequent potential for host toxicity. The commonly used polyene and triazole antifungals, which target fungal cell membrane sterols, also affect the stability and production of mammalian cell membrane cholesterol. The recently developed echinocandins are more specific for fungal targets, however they are ineffective in the treatment of Histoplasma capsulatum and Cryptococcus neoformans, leaving the host-toxic polyenes and triazoles as the only methods for treatment of infections caused by these pathogens. From a library of small molecules with structural similarities to purines (e.g., ATP/GTP, NADP, etc.), we identified a series of thiazole-based compounds that have potent antifungal activity against Histoplasma capsulatum and Cryptococcus neoformans. Importantly, these compounds inhibit not only fungal cells in culture but also fungal cells that reside within mammalian host cells following infection. Treatment of Histoplasma-infected macrophages with the thiazole-based antifungals protects host cells from Histoplasma- induced cell death. To mature the top hit antifungal thiazole into a lead candidate for drug development and to better understand its mode of action, this research proposal seeks to identify the cellular target(s) of the antifungal thiazole using affinity and chemical proteomics and to provide initial n vivo efficacy and toxicity studies using an animal model. In addition, derivatives of the thiazole will be prepared and tested to define the structural features necessary for antifungal activity and to improve its chemical properties and maximize antifungal potency.